What is V2X communication? Creating connectivity for the autonomous car era

Unless you’re a hardcore vintage car enthusiast, you’ll have noticed that vehicles are becoming increasingly connected, both to each other and to the outside world.

With car operating systems running everything from infotainment to autonomous driving, vehicles are becoming ever more intelligent and less reliant on human operation. Vehicle users stand to benefit from safer, greener, and more efficient journeys thanks to copious sensors and onboard connectivity, while car manufacturers, tech companies, and communications providers have a whole new market to compete in.

V2X, which stands for ‘vehicle to everything’, is the umbrella term for the car’s communication system, where information from sensors and other sources travels via high-bandwidth, low-latency, high-reliability links, paving the way to fully autonomous driving.

There are several components of V2X, including vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-pedestrian (V2P), and vehicle-to-network (V2N) communications. In this multifaceted ecosystem, cars will talk to other cars, to infrastructure such as traffic lights or parking spaces, to smartphone-toting pedestrians, and to datacentres via cellular networks. Different use cases will have different sets of requirements, which the communications system must handle efficiently and cost-effectively.

What kind of transportation experience can we expect in a V2X world? Researchers from Huawei’s German Research Center in Munich outlined their vision in a recent paper:

(1) User hails an on-demand car via an app; (2) Vehicle self-drives or is tele-operated to the user, whose personal transportation app connected over the mobile radio network adjusts the car to selected presets; (3) Vehicle searches for the platoon best suited to the user’s preferences and performs cooperative maneuvering to join the selected platoon, saving energy by allowing car following at very short gaps; (4) Two-way navigation guides the vehicle around a congested stretch of road; (5) User takes control to exit the highway and drive on a particularly scenic road suggested by the connected navigation system; (6) Vehicle drops the user off at the destination; (7) The vehicle self-drives, either to an automated parking lot (7a) or to a different user (7b).

The Huawei researchers note that: “While this example might seem far into the future, most of the technology needed to enable it (high precision maps, real time traffic information, sensors inside the vehicle such as radars, cameras, ultrasonic, etc.) are either already available or will be in the near future. The most prominent missing component is a high reliability, low latency communications system.”

As with any new field of technology, there are competing standards in play for V2X.

IEEE 802.11p

The original V2X standard is based on a Wi-Fi offshoot, IEEE 802.11p (part of the IEEE’s WAVE, or Wireless Access for Vehicular Environments program), running in the unlicensed 5.9GHz frequency band. IEEE 802.11p, which was finalised in 2012, underpins Dedicated Short-Range Communications (DSRC) in the US, and ITS-G5 in the European Cooperative Intelligent Transport Systems (C-ITS) initiative.

Functional characteristics of 802.11p include short range (under 1km), low latency (~2ms) and high reliability — according to the US Department of Transportation, it “works in high vehicle speed mobility conditions and delivers performance immune to extreme weather conditions (e.g. rain, fog, snow etc.)”. Essentially, 802.11p extends a vehicle’s ability to ‘see’ the environment around it, even in adverse weather.

IEEE 802.11p is not dependent on the presence of cellular network coverage, and solutions — onboard units (OBUs) and road-side units (RSUs) — are available now from silicon vendors including NXP, Marvell, Renesas Electronics, and Redpine Signals.

Cellular V2X

A key advantage of C-V2X is that it has two operational modes which, between them, cover most eventualities. The first is low-latency C-V2X Direct Communications over the PC5 interface on the unlicensed 5.9GHz band, and is designed for active safety messages such as immediate road hazard warnings and other short-range V2V, V2I, and V2P situations. This mode aligns closely with what’s offered by the incumbent IEEE 802.11p technology, which also uses the 5.9GHz band.

Image: Qualcomm

The second mode is communications over the Uu interface on the regular licensed-band cellular network, and can handle V2N use cases like infotainment and latency-tolerant safety messages concerning longer-range road hazards or traffic conditions. Because it doesn’t use cellular connectivity, IEEE 802.11p can only match this mode by making ad hoc connections to roadside base stations.

The current C-V2X Rel-14 specification — part of the global 3GPP Rel-14 standard and LTE Advanced Pro — was finalised in March last year, while Qualcomm’s first C-V2X chipset, the 9150, was announced in September and is expected to be available for commercial sampling in the second half of 2018. Qualcomm also introduced a C-V2X Reference Design featuring the 9150 C-V2X chipset with integrated GNSS capability, an application processor running the ITS V2X stack and a Hardware Security Module (HSM). Compared to IEEE 802.11p, C-V2X is several years behind in terms of deployment in the V2X market.

Here are some technical and use case comparisons between 802.11p and current and future C-V2X specifications (from C-V2X supporter Qualcomm):

Image: Qualcomm
Image: Qualcomm

Testing of current C-V2X technology is underway with Ford in the US, with Audi and Groupe PSA in Europe and with SAIC in China. Going forward, the C-V2X roadmap will include 5G NR (New Radio) features such as high throughput, wideband carrier support, and high reliability.

This technological evolution, combined with estimates that 45 percent of the estimated 2.2 billion cellular connections in 2025 will be in the connected car sector, should provide strong arguments in favour of C-V2X over 802.11p as the basis for V2X. However, doubt has been expressed over whether C-V2X will be able to leverage the presence of standard cellular modems in cars due to different safety requirements and technology needs.

Which standard will win?

IEEE 802.11p has the advantage of earlier development and deployment, and therefore incumbency. On the other hand, C-V2X offers arguably better performance, the ability to employ both direct and network-assisted communication, and an evolutionary path to 5G.

This is not just an arcane technology standards debate: the stakes are high, with the incumbent 802.11p still the favourite in many regions. In Europe, this prompted the GSMA to make its position clear in a September 2017 briefing paper:

“The GSMA is concerned that Europe’s rollout plans of C-ITS do not take into account the very high potential of C-V2X. The GSMA notes that the European Commission wishes to prevent a fragmented deployment of two different vehicle-to-vehicle communications. It therefore clearly favours the ‘incumbent’ technology, 802.11p, that forms the radio standard within the C-ITS framework called ITS-G5. The Commission is considering whether to announce a European Delegated Act on C-ITS soon, which would mean that by 2019 any future technology on the market would need to be able to communicate with cars deployed with 802.11p technology over their entire lifetime. This would, effectively, lock-in 802.11p as the central communications V2X technology for decades.”

Volkswagen has already thrown its (considerable) weight behind 802.11p, which it will start fitting on selected models from 2019.

It’s possible that 802.11p and C-V2X will coalesce in future, combining the strongest points of each technology. Indeed, the researchers at Huawei’s German Research Center also expect upcoming technologies such as high-frequency (eg 60GHz), high-bandwidth mmWave and VVLC (Vehicular Visible Light Communication) “to be incorporated in the 5G V2X access network architecture to support specific V2X use cases.” This will allow the industry to present regulators with solutions that maximise the benefits for all vehicle users.

Here are some use case requirements considered by the Huawei researchers, and their assessment of the ability of different technologies to support them:

Use Case Type

V2X Mode

End-to-End Latency

Reliability

Data Rate per vehicle (Kbps)

Comm. Range

Cooperative Awareness

V2V/V2I

100ms-1s

90-95%

5-96

Short to medium

Cooperative Sensing

V2V/V2I

3ms-1s

95%

5-25000

Short

Cooperative Maneuver

V2V/V2I

3ms-100ms

99%

10-5000

Short to medium

Vulnerable Road User

V2P

100ms-1s

95%

5-10

Short

Traffic Efficiency

V2N/V2I

1s

90%

10-2000

Long

Teleoperated Driving

V2N

5-20ms

99%

25000

Long

Use Case Type

LTE-V2X

802.11p

mmWave

VVLC

Cooperative Awareness

Emergency Vehicle Warning

Forward Collision Warning

✔︎✔︎

✔︎✔︎

✔︎✔︎

✔︎✔︎

✘

✔︎

✘

✔︎

Cooperative Sensing

See-through

Sensor sharing

✔︎

✔︎

✔︎

✔︎

✔︎✔︎

✔︎

✔︎

✔︎

Cooperative Maneuver

Platooning

High-Density Platooning

Cooperative Adaptive Cruise Control

Cooperative Intersection Control

✔︎✔︎

✘

✔︎

✔︎

✔︎

✘

✔︎

✔︎

✔︎

✘

✘

✘

✔︎

✘

✘

✘

Vulnerable Road User

✔︎

✔︎

✘

✘

Traffic Efficiency

✔︎✔︎

✔︎

✘

✘

Teleoperated Driving

✔︎

✘

✘

✘

Tables: Use Cases, Requirements, and Design Considerations for 5G V2X (Huawei German Research Center, 2017)

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